Reaction Behavior And Effects Of Impurity Components In The Calcification-Oxidative Roasting Of Chromite Ore

In the traditional method for producing chromium salts of chromite by alkali decomposition,there are problems such as high consumption of auxiliary materials and large discharge of chromite ore processing residue.Therefore,a clean production method of chromium salts based on calcium and ammonium auxiliary material circulation was proposed.One of the keys is that chromium in chromite is converted into soluble chromium-calcium compounds in the calcification-oxidation roasting process of chromite,however,the impurity components such as iron and aluminum in chromite have a significant effect on the roasting process.Based on the previous research on the formation of chromium-calcium compounds in the calcification-oxidative roasting process,the reaction behavior and influence of impurities in the roasting process were systematically studied in this paper.The main conclusions were listed as follows.（1）The thermodynamics of the reaction between impurity components such as Mg O,Fe₂O₃,Al₂O₃,and chromium-calcium compounds were systematically analyzed.The results showed that Mg O does not react with Ca Cr O₄,Ca₃Cr₂O_8,and Ca₅Cr₃O_12.5 under the condition of calcification-oxidation roasting of chromite.However,Fe₂O₃ and Al₂O₃easily react with calcium-containing components to form calcium aluminate and calcium ferrite under high-temperature conditions,and Fe₂O₃ and Al₂O₃ can react with Ca₃Cr₂O₈ and Ca₅Cr₃O_12.5 to form low Ca/Cr compounds Ca Cr O₄ and Ca Cr₂O₄.Furthermore,the influence of impurity components on the conversion of chromium-calcium compounds was clarified in the roasting experiment of impurity components and chromium-calcium compounds.（2）The reaction behavior of the formation of chromium-calcium compounds in the calcification-oxidative roasting process of different chromium spinels was studied.The regularity of Mg O·Cr₂O₃ and Ca CO₃to form chromium-calcium compounds in the oxidative roasting is similar to Cr₂O₃,and Ca Cr O₄ is easily formed under low-temperature conditions.However,the chromium spinel containing impurity elements（Mg O·0.5Cr₂O₃·0.5Al₂O₃ and Mg O·0.5Cr₂O₃·0.5Fe₂O₃）forms chromium-calcium compounds very slowly in the calcification-oxidation roasting at low temperature.Although the chromium spinel containing impurity elements can be quickly converted into chromium-calcium compounds at higher temperatures and high calcium carbonate dosage conditions,it is difficult to form Ca Cr O₄,and the main products are Ca₃Cr₂O₈ and Ca₅Cr₃O_12.5.The influence of the impurity components in chromium spinels on the formation of chromium-calcium compounds in the roasting process was clarified,which further explains that Ca Cr O₄ is difficult to form in the calcification-oxidation roasting process of chromite.（3）Based on the study of the effect of impurity components on the calcification-oxidation roasting process of chromium spinel,the effects of adjusting the proportions of materials in the raw meal and secondary roasting of clinker on the conversion of chromium in chromite into easily leached chromium-calcium compounds were explored.A method of two-stage roasting to improve the yield of chromium from chromite ores was proposed,which could realize a 94%yield of chromium.